1. Field of the Invention
This invention relates generally to actuators for positioning data sensing heads in a rotary disk drive and specifically to a modular actuator assembly made up of a combination of standardized components.
2. Description of the Related Art
Data storage technology has followed a trend of increasing storage capacity while also decreasing the physical volume occupied by such capacities. Introduction of ever more powerful computer microprocessors and software has contributed to increasing market pressures for ever cheaper, ever larger capacity and ever smaller physical profiles in disk drives. Storage device manufacturers strive to achieve any possible incremental cost savings that can be reasonably achieved without loss of technical performance.
A key aspect in reducing manufacturing costs for disk drives is improving the manufacturability of disk drive components. Among others, disk drive components include read/write heads for recording and retrieving data from a storage disk and a head actuator assembly for positioning the heads with respect to the storage disk. Such actuators may be either linear or rotary, each having specific advantages for the particular application. In magnetic disk drives, the rotary or "swing-type" actuator assembly is most commonly used. The over-riding requirement for advancing the actuator assembly art is widely believed to be improved ease of manufacturability without losing reliable performance. FIG. 1 represents a typical swing-type actuator assembly 10 known in the art as the E-block actuator assembly.
As seen in FIG. 1, actuator assembly 10 includes an E-block 12 fabricated by machining an aluminum or magnesium casting or extrusion. E-block 12 includes one or more actuator arms exemplified by actuator arm 14. A head suspension (not shown) is fixed to the end of each such actuator arm at a position exemplified by the swaging hole 16 on actuator arm 14. E-block 12 also includes a pivot bore hole 18 disposed to receive a pivot bearing assembly (not shown) for supporting rotation of actuator assembly 10 about a pivot axis 20. As actuator assembly 10 rotates back and forth about pivot axis 20, each of several read/write heads (not shown) disposed on suspensions (not shown) fixed at the several actuator arm swaging holes exemplified by swaging hole 16, swings across the data recording tracks of a rotary magnetic disk (not shown) in the manner well-known in the art for such swing-type actuator assemblies.
E-block 12 is usually fabricated from cast or extruded aluminum or magnesium that is machined to provide the requisite attachment points for head suspensions, pivot bearing assembly, latch components and voice coil motor components. Head suspensions are usually attached to the actuator arm tips by swaging or staking through machined holes in the E-block arms (e.g., the hole at location 16). Accurate maintenance of the specified dimensional relationships of E-block 12, head suspensions and heads is very important to proper disk drive performance.
The actuator assembly 10 shown in FIG. 1 suffers from well-known cost and manufacturability problems. E-block 12 is expensive to manufacture. The alignment and seating of the head suspensions and heads must be manually supervised by a technical worker, thereby increasing assembly manufacturing costs and reducing manufacturing yield.
Practitioners in the art have addressed these problems with many proposals for incremental improvement to the actuator assembly design typified by actuator assembly 10 in FIG. 1. For instance, In U.S. Pat. No. 5,382,851, Robert Loubier discloses a different swing-type actuator assembly of the type exemplified by the actuator assembly 22 in FIG. 2. Actuator assembly 22 encapsulates a coil carrier 26 and individual metallic actuator arms exemplified by the actuator arm 24 into a central plastic body 28 to eliminate the heavy central portion 30 (FIG. 1) of E-block 12. But a coil-block joint flexure problem known in the art is exacerbated because most of E-block central portion 30 is replaced with plastic, thereby perhaps introducing more flexibility in the alignment between coil carrier 26 and the actuator arm plurality 32. Also, pivot-axis runout is increased because of increased flexibility at the inner surface of the bore hole 36. Loubier molds a separate metal journal 34 into plastic pivot body 28 at bore hole 36 in an attempt to rigidly couple pivot axis 20 to body 28 and to electrically couple actuator arm plurality 32 for static charge purposes. Disadvantageously, the precise alignment of actuator arm plurality 32 needed for this configuration requires jigging or drilling steps additional to those required with monolithic aluminum E-block configurations.
Thus, as is well known in the art, the requirements for head actuator assembly rigidity and alignment precision often require solutions that trade for increased actuator inertia and reduced manufacturability. Even the partially molded head actuator assembly 22 shown in FIG. 2 requires human supervision of alignment during manufacture.
The known actuator assembly fabrication techniques illustrated in FIGS. 1-2 are not convenient for use in manufacturing a series of multi-platter disk drives of various numbers of disks. Each actuator assembly is optimized for use in only one specific disk drive design. For instance, consider that a four-arm actuator assembly (with six head suspensions) is specially designed and assembled for use in a three-platter disk drive. Although the four-arm actuator assembly could arguably be used without modification in a one- or two-platter disk drive by omitting the unused head suspensions, the result gives unnecessarily high inertia (mass) and component count (cost). That is, by simplifying manufacturing procedures through using a, for example, four-arm actuator assembly design in all one-, two-, or three-platter disk drive products, any prospective manufacturing savings from eliminating multiple actuator designs are lost to unnecessary and unwanted actuator inertia (lower performance) and component count (higher cost) in many of the disk drive designs. No particular actuator assembly design can be used in multiple disk drive designs without sacrificing either performance or cost or both.
Various practitioners have proposed other solutions to the actuator assembly manufacturability problem. For instance, in U.S. Pat. No. 5,410,794, Larry Tucker discloses a manufacturing tool for holding head-stack assembly (HSA) components during manual assembly. Tucker's tool provides for positioning the head-stack components including two pairs of actuator arm assemblies, associated spacers and a flat coil member, in an aligned relationship to permit a pivot bearing to be inserted through an opening in each component adapted to receive the bearing. Tucker neither considers nor suggests means for self-aligning assembly of several different actuator designs using standardized components.
In U.S. Pat. No. 5,363, 262, George Drennan discloses an actuator assembly in which only flexible integral load beams are used in the arm-stack structure. The load beams are assembled in a stack on a tubular actuator member together with the moveable coil member of the actuator motor or other actuator drive mechanism, and after alignment are secured to the tubular member to form a separate actuator assembly. Drennan's invention eliminates unnecessary arm-stack and actuator structure between the HSA and the moving coil carrier portion of the actuator motor, thereby eliminating substantial inertia from the actuator. However, Drennan neither considers nor suggests means for the self-aligning assembly of standardized components to form one of a variety of different actuator designs.
In U.S. Pat. No. 5,404,636, Stefansky et al. disclose a disk drive actuator assembly method similar to Drennan's teachings. Stefansky et al. teach a method for assembling an actuator from a selection of modular components by stacking a first and a second actuator arm in an orientation where the axis of the arms are non-parallel, inserting comb assembly between the first and second arms, rotating the arms about the assembly member until disposed in parallel, and finally securing the arms against rotation relative to one another. Although Stefansky et al. for the first time proposed the use of standardized arm and actuator components as one method for improving manual alignment of head suspensions during staking to the E-block in the assembly process, they neither consider nor suggest means for self-aligning of components during the assembly of one of several different actuator designs.
In U.S. Pat. No. 5,299,082, Ananth et al. disclose an apparatus and method for pre-loading the outer most head suspensions in an actuator HSA to compensate for the absence of a second head suspension in each of the two outer actuator arms. Thus, Ananth et al. propose a solution to the pre-load imbalance problem arising from the presence of two head suspensions fixed to each of several interior actuator arms and a single head suspension attached to each of two outer actuator arms in a HSA. However, Ananth et al. neither consider nor suggest solutions to the modular assembly problem nor to the problem of using standardized components to manufacture several different actuator assembly designs.
In U.S. Pat. No. 5,070,423, David Gloski discloses a high-performance actuator array employing independently-driven reciprocating carriage arms. Although Gloski's actuator array uses modular components, he neither considers nor suggests the self-aligning automated manufacture of rotary actuator assemblies.
In U.S. Pat. No. 5,293,290, Owens et al discloses a modular, stackable, linear actuator using embedded coil carriages. Like Gloski, Owens et al. neither consider nor suggest solutions to the rotary actuator manufacturability problem.
Other solutions to the twin head suspension pre-load balancing problem are suggested in U.S. Pat. No. 5,381,289 by Richard Fiedler and in U.S. Pat. No. 5,390,058 by Akihiko Yamaguchi. Like Ananth et al., neither Fiedler nor Yamaguchi consider or suggest solutions to the self-aligning modular actuator manufacturability problem.
Without solutions to the increased manufacturing complexity needed to reduce actuator inertia without losing requisite rigidity and for other disadvantages of the molded plastic actuator assembly known in the art, practitioners are obliged to accept unwanted new fabrication costs to obtain a desired reduction in actuator rotational inertia. Certain of these unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below.